@99PerCent turned me on to:
They’re not particularly cheap for folks like us but definitely fair/reasonable. They do custom and pre-fab & variety of colors & meshes.
2nd choice: harborfreight mesh tarps; they’re cheap but the packaging says 65-70% shade & I’d say that’s probably an overestimate but solor-angle-to-surface makes a big difference. It’s very hard to get a perfect exposure from sunrise to sunset & season to season… 'Still conjuring up an ideal shape in my mind & it’s not conducive to 2x4’s & square things. 
